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Micro Processor Interview Questions - Part 5

What are the internal devices of 8255 ?

The internal devices of 8255 are port-A, port-B, port-C. The ports can be programmed for either input or output function in different operating modes.

What is USART ?

The device which can be programmed to perform Synchronous or Asynchronous serial communication is called USART (Universal Synchronous Asynchronous Receiver Transmitter). Eg: INTEL 8251

What is scanning in keyboard and what is scan time ?

The process of sending a zero to each row of a keyboard matrix and reading the columns for key actuation is called scanning. The scan time is the time taken by the processor to scan all the rows one by one starting from first row and coming back to the first row again.

What is programmable peripheral device ?

If the function performed bythe peripheral device can be altered or changed bya program instruction then the peripheral device is called programmable device. It have control register. The device can be programmed by sending control word in the prescribed format to the control register.

What is baud rate ?

The baud rate is the rate at which the serial data are transmitted. Baud rate is defined as (The time for a bit cell). In some systems one bit cell has one data bit, then the baud rate and bits/sec are same.

What are the tasks involved in keyboard interface ?

The tasks involved in keyboard interfacing are sensing a key actuation, Debouncing the key and generating key codes( Decoding the key). These tasks are performed software if the keyboard is interfaced through ports and they are performed by hardware if the keyboard is interfaces through 8279.

How a keyboard matrix is formed in keyboard interface using 8279 ?

The return lines, RL0 toRL7 of 8279 are used to form the columns of keyboard matrix. In decoded scan lines SL0 t0SL3 of 8279 are used to form the rows of keyboard matrix. In encoded scan mode, the output lines of external decoder are used as rows of keyboard matrix.

What is GPIB ?

GPIB is the General Purpose interface Bus. It is used to interface the test instruments to the system controller.

Advantages of differential data transfer ?

  • Communication at high data rate in real world environment.
  • Differential data transmission offers superior performance.
  • Differential signals can help induced noise signals.

    What is difference between Microprocessor and Microcontroller ?

    Microprocessors generally require external components to implement program memory, ram memory and Input/output. Intel's 8086, 8088, and 80386 are examples of microprocessors. Micro controllers incorporate program memory, ram memory and input/output resources internal to the chip. Microchip's pic series and Atmel's AVR series are examples of micro controllers

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